Liquid crystal cells are commonly used as part of liquid crystal displays associated with electronic devices such as televisions, watches, calculators, computer displays, and mobile telephones. FIGS. 1A and 1B illustrate, respectively, a side elevation and a plan view of an embodiment of a liquid crystal (LC) display cell 100. The LC display cell 100 comprises a die 102 having a dam 106 formed on a surface 104 thereof. The dam 106 forms a sealed perimeter around a portion of the surface 104. A transparent cover 108 having surfaces 112 and 113 is attached and sealed around its perimeter to the dam 106 such that a small portion of the cover 108 overhangs the dam. The surface 104 of the die 102, the dam 106, and the transparent cover 108 define a sealed volume 116 of depth d that is then filled with liquid crystals to complete the liquid crystal cell. In one embodiment the volume 116 has a depth d of approximately one micron, although the distance d can range from a distance on the order of millimeters to a distance on the order of micrometers. In the embodiment shown, the LC cell 100 is attached to a substrate 103, which in one embodiment is a ceramic substrate but in other embodiments may be something different. The ceramic substrate 103 can include other components not shown here, such as heat sinks, electronic circuits and/or components, and the like. The die 102 is electrically connected to the substrate 103 via bond pads 120 and wire bonds 124. The overhanging portion of the transparent cover 108 is electrically connected to the ceramic substrate, or to some circuitry thereon, by a crossover ground 126.
FIG. 1C illustrates the structure of the transparent cover 108 of the LC cell 100. The cover 108 includes a transparent substrate 110 with an alignment layer 117. The alignment layer is applied to a surface 115 of the substrate 110. Although not shown, a transparent electrically conductive layer is usually applied to the substrate; the conductive layer is commonly applied to the surface 115 of the substrate (i.e., it is sandwiched between the substrate 110 and the alignment layer 117), but in other embodiments can also be applied to the outer surface 113 of the substrate. The electrically conductive layer functions as an electrode, so that an electric field can be applied to the liquid crystals within the volume 116 to cause the liquid crystals to alter their orientation and thus alter the display. In one embodiment, the electrical signal is routed through the die via traces connected to the bond pads 120 and flows through the liquid crystal distance d to the electrically conductive layer as it aligns the liquid crystals to display the image. The electrically conductive layer is grounded back to the substrate 103 via a cross over ground connection 126. The side of the alignment layer 112 that is in contact with the liquid crystals in the volume 116 usually includes a plurality of microgrooves 118 therein. The purpose of the microgrooves 118 is to provide an initial alignment to the liquid crystals within the volume 116; in most cases, the initial alignment of the liquid crystals is parallel to the microgrooves. It is preferable that the initial alignment of the liquid crystal has a substantial penetration depth—that is, the alignment layer should cause the liquid crystals in the volume 116 to become initially aligned in the desired direction throughout the entire depth d of the liquid crystal (see FIG. 1A).
Currently, the microgrooves 114 in the alignment layer are formed by hand-rubbing the layer 108 with some sort of abrasive material such as rayon pile cloth with a 600 μm fiber length, 15 μm fiber diameter and a thread count of 32,000 thread per square centimeter. In addition to the less-than-ideal quality of the resulting microgrooves, the hand-rubbing method for forming the microgrooves has several other disadvantages. Among other things, it does not result in a uniform and consistent groove pattern, which can affect the penetration depth of the alignment. Hand rubbing is also time intensive and labor intensive, which leads to increased costs for liquid crystal displays. The hand-rubbing method is difficult to adapt to a manufacturing environment, and also makes it difficult or impossible to realize economies of scale in the manufacturing of the liquid crystal displays.